86 300E power loss at speed - PeachParts Mercedes-Benz Forum

A264172 · #1 01-29-2006, 12:15 AM

Happened twice today. Car fully warmed up temp (90C+). Both incidents were on highway at aprox.60 mph. Economy gage pegged in red. Oil pressure good (pegged). RPM's responded to pedal but produced no power. As I would pull over and pump the gas to get a little further up the berm I would get slight little bits of power transmission. Let it sit for a couple minutes and it started right up and did not loose power till the next 25mile highway trip. Both times uphill.

Looked for vacuum leaks between the two stalls but the symptoms were not present during testing. Replaced the cracked crankcase to intake manifold hose.

Thinking vacuum leak...

Or crankposition sensor (do rpms stay under control of accelerator pedal during cps related stalling?)

Other possibilitys... coil?... valve cover gasket?... ???

Any suggestions, ideas, or experiences appriciated.

t walgamuth · #2 01-29-2006, 08:19 AM

like fuel starvation to me. are you sure you have fuel? could be a sender failure. also could be junk in your fuel and plugged filter or strainer. air filter is possible but less likely.

good luck

tom w

dave_rose69 · #3 01-29-2006, 09:28 AM

Marty: You have one of those hair pulling intermittant problems which requires some sophisticated diagnostic routines, however if you are really going to try and fix this problem yourself, stay with this forum and be ready to invest in some diag. equipment. Do these things: 1. Check fuel pressure at fuel distributor or spray bar inlet rail, buy or borrow a fuel pressure gauge that goes to at least 100PSI. You need a "T" fitting to do this test, 3/8" on top of the "T" side, 5/16" to the pressure gauge side. You need a steady 75 to 85 lbs. PSI for good running. Also check the volume, its about a 1 quart delivery in 30 seconds. Hose clamp all the fittings, as the 80lbs of pressure will surely pop a test hose off its fitting. If your pressure drops at any time during the loss of power, replace or service the fuel pump relay first. A tell tale test is to run a pair of wires from the pumps and into a VOM, set it for DC volts. you must have 13.XX volts solid at that point, if it drops down during the power loss, its the pump relay. If you have a module on the left side of your battery compartment with a knob marked 0/1 on it, this is the MAS module. This knob actually retracts the module from its socket.The fuel pump relay is inside of this unit. IT CAN BE SERVICED. If you have a seperate relay for the pumps, just find it and change it. If there is no power droppage to the pumps, do an entire fuel sys. overhaul. Clean Pickup screen, (large allen socket plug in middle of tank, you will need a new O-ring), main filter, check fuel accumulator, fuel pressure regulator. If you monitor the fuel pressure directly from the pumps and it fails, its the pump (s) or accumulator. if it drops when hooked between the inlet and pressure regulator, its the regulator. Generally, the fuel sysems are bullet proof, and If you find no faults with pump power and pressure, I would do: Ignition overhaul, plugs cap rotor wires, and coil... Also replace your OVP relay. The MB Ign coils are the worst, especially the older ones with sheet metal stamped center sections. Go look at the color of your spark, it must be whitish blue, not orangy red...... be patient, you'll find something eventually.....
If its the CPS, the tach will drop down even though the engine is running. It tests: 750 to 780 ohms, and .480 to .505 Volts AC during cranking. They do sometimes fail even if they test good with the VOM. If you have no spark at any time, it could be the CPS. Also check the rotor adaptor plate retainer bolt, these adaptors get loose too.

go here to learn where your modules and relays are located
http://mb.braingears.com
Go here for parts: www.***************
http://catalog.peachparts.com/
dave
dave_rose69@yahoo.com

A264172 · #4 01-30-2006, 02:47 PM

Thanks for that guys.

Ill post back when I get some preliminary readings.

Can I buy 10' of regular rubber fuel hose to extend the gage into the cabin to try and recreate the stall? Or will I need a teflon hose for the higher pressure?

Ill buy some fittings and get started when I have a little time.

Thanks again.

dave_rose69 · #5 01-30-2006, 05:39 PM

Go to a parts place where they sell fuel line by the foot. 5/16 to 3/8" ID is good. Gates brand seems the most flexable. You must use hose clamps on every fiitting, dont forget....What system does your car have? Does it have mechanical fuel injection "KE" Hows your electrical systems voltage, at least 13.5 volts? Do you have the original Ign coil in the car? Do the electrical testing first....

Dave.....

#6 01-30-2006, 05:52 PM

I would first replace the fuel filter and see if the problem remains. If it does, disconnect the EHA harness and see if the car drives okay. If it does, then the trouble is in the EHA, very likely related to the O2 sensor.

Is the check engine light on? Check the O2 sensor connector underneath the passenger side front floor mat.

Good luck,

A264172 · #7 01-30-2006, 05:57 PM

It has CIS E

This being an intermitant problem (didn't happen yesterday or today) I am thinking of rigging up the fuel pressure gage as you suggest and taking it out for a 20 mile drive to try and duplicate it. Where would be a logical place for my t fitting?

I have a known leaking EHA. Would this be able to produce these symptoms?

A264172 · #8 02-13-2006, 06:54 PM

Quote:

Originally Posted by dave_rose69

Marty: ...check fuel accumulator, ... If you monitor the fuel pressure directly from the pumps and it fails, its the pump (s) or accumulator. ...

Dave,
How would accumulator failure manifest itself in power loss?

I ask this because I have read that a secondary function of the accumulator is ti supress pulseing noises of the fuel pump, and I have been hearing pulsing noises under load.

dave_rose69 · #9 02-13-2006, 08:38 PM

The fuel accumulator, acts as a reverse flow check valve, but is more of a reverse pressure regulator. It allows the fuel system to hold pressure, from the delivery side (tank and pumps) and insures quick start ups, by keeping the fuel pressure up, even when the pumps have been off for many hours. If the accumulator is letting go, (leaking down) while driving, the end result is a lowered fuel pump pressure to the fuel distributor and its pressure regulator. The only way to see this, is to drive the car and monitor the fuel pump pressure remotely via a gauge brought into the car. I do suggest a helper friend to watch the gauge, as not to be destracting while you are driving. You can block the return line from the accumulator, but you run the risk of introducing contamination into your fuel system, if you dont do it in surgically clean way. If you havent already checked your ignition coil out, do so, you might be suffering from this power loss due to ignition break down under compression from a weak coil....Check the color of your spark....!!!! Any unusual noise from the pumps can be traced first to a clogged pick up screen in your tank, It makes a sorta slurping sucking noise, like when you pull soda from a straw in an almost empty can, or, a squishing sound, (over pressure) from trying to suction through a very clogged filter. Or, maybe the motors armature bushings in the pump are shot, rare until around 250,000 miles. Usually poor power problems stemming from a clogged fuel filter, lessens when you add more fuel into the tank. The extra fuel now available, via gravity, helps push the fuel better into the pump system.

A264172 · #10 02-25-2006, 07:07 PM

New fuel filter (and spark plugs) did not help.

It does not seem to be related to how much fuel in tank.

The one thing that strikes me as some kind of clue is: as it starts loosing power, if I quickly flip the key (ignition switch) to position I then back II (on) it regains power for a short time... like 15 seconds aprox.

I will continue to figure out these tests and begin to impliment them... and post updates as they become available.

davestlouis · #11 02-25-2006, 08:36 PM

to clarify, you had a post that referred to clicking from the dash...that was what struck me as odd, because mine is giving me the same symptom.

A264172 · #12 02-25-2006, 08:44 PM

I understand dave.
I think it may be due to vacuum loss caused by not enough combustion due to the fuel delivery problem. Wish I knew for sure, it's a frustraiting mess... but it gives me a hobby to pursue.

Thanks for the tip ande......

A264172 · #13 02-27-2006, 10:27 AM

Re-did the vacuum line from the fuel accumulator to the breather hose and the rubber on either side of the ICV to no effect.

I got a good clue on the test drive though. After it started loosing power again I disconected the EHA again as larry suggested eariler. (it didn't stall or stutter the first time I did that but I forgot to test it again that way because starting the car in the AM in February in Pittsburgh is not really an option without the EHA). So it was stalling every 20 seconds, pulled over and took off air cleaner and disconected the EHA, put everything back together and took it out and around for 55 miles... no stalling!

Now to figure out where the bad input is comming from.

dave_rose69 · #14 02-27-2006, 06:57 PM

If Im not mistaken, the KE control module cycles the EHA to maintain correct fine end fuel metering from the fuel distibutor. The KE module adjusts the duty cycle to the EHA via the oxygen sensor voltage output into the KE unit. So, if the O2 sensor is malfunctioning, the EHA will not be regulated properly, or if the KE unit is not being powered correctly, or if it has a cold solder spot on its pc board, this can also cause the failure of the EHA to be properly regulated. I have recently reflowed all my control units in my 300TE, (KE unit and MAS unit) there were some cold spots, but not many, and my car happens to be quite prestine as it was always garaged. When you get the engine to run normally after a quick power down and quick power up routine, (ignition switch off-on), it could be the OVP relay getting a better bite on its contacts for a few moments, until it looses its contacts integrity, or perhaps the KE unit is starting from a center point setting referrence that is governed by its firmware. A newer VOM with a DC volts duty cycle percentage setting, might help you see if you are indeed getting the correct control signals from the KE module. If you know someone who is an electronic repair person, have him re-flow all the sub boards and pinouts in the KE unit, and take a voltage reading from the O2 sensor to confirm it is working. (Its around .450 to .500 milivolts) If you havent changed the OVP relay yet, nows the time to try at least a known good one to see if it is a power problem to the KE unit.
Dave...

A264172 · #15 02-28-2006, 11:25 PM

Larry you called it.
Checked the duty cycle today and got a reading of 90-92% (I had checked it last week and it was 55% so I thought it was OK) exposed the O² connector and waited for the bogging. it was kind of harry stearing with my knee on the highway as she was dieing and leaning over with both hands to pull the plug on the O² control, but after I did the stall stalled out, power came back, and I laughed and smiled the rest of the way home. I replaced it almost one year ago so I thought it was good. Guess I had better get to those valve seals this summer, it must be taking a real beating back there.
Dave Rose,
I can't thank you enough for the elaborate insight into the fuel delivery system. I feel ready to delve into it and have, with your help, assembeled most of the fittings, hose, and gages that I will need to do so. Thanks for taking the time.
I think will go to ford and get the proper conector so I can just snap that 91' mustang 302 sensor right into the system. And I'll update as this gets finished up... and thanks again.